1. Field of the Invention
This invention generally relates to improving cast aluminum wheel production and improved cast aluminum vehicle wheels More particularly, the invention relates to process improvements that include shortening of cycle times, conserving resources and achieving energy saving effects, as well as modification of microstructures and mechanical properties of cast aluminum vehicle wheels.
2. Description of Related Art
Vehicle wheels made out of aluminum or aluminum alloys can be manufactured according to various methods. By one approach, the wheel is cast from molten aluminum material poured into a metal mold. By another approach, the wheel is forged from a billet of heated aluminum or aluminum alloy. By another approach, the wheel can be “spun” to a desired basic shape by the application of forging discs or rollers into a thin sheet of graded aluminum sheet. Such can be conducted in association with the introduction of pressures, either high or low, onto a molten alloy in the mold cavity. Flow-forming technology has improved on older “spinning” procedures. Additionally, aluminum vehicle wheels can be of a mono-block or multi-piece construction, depending upon the design requirements for the wheel being manufactured.
It can be considered that most aluminum vehicle wheel manufacturing techniques can be classified as either a casting approach or a forging approach. When compared with a forged wheel, a cast wheel has the advantages of facilitating design flexibility and lower cost. However, mechanical properties such as strength and favorable elongation characteristics are restricted by coarseness of the micro-grain structure of cast aluminum wheels and other metallurgical properties. Often, in order to achieve required strength, the rim portion of a cast wheel needs to be thicker than might be desired for design reasons, resulting in a wheel of relatively heavy weight, or at least of a weight that must be heavier than that needed to achieve certain desired design effects.
Heretofore, the coarse microstructure disadvantage of casting has been lessened by implementing a so-called spinning process The spinning process applies disc rollers to the cast wheel while it is in the plastic deformation stage in order to introduce high axial pressure onto the surface of the cast wheel. This spinning process has been found to improve the mechanical properties of the cast wheel. However, conventional cast wheel production temperature processes, even when flow forming is practiced in the conventional manner, are particularly wasteful of energy due to temperature changes needed for stabilizing microstructure and for refining grain size during various stages of the process, including cooling, heat treatment and quenching.
Energy inefficiencies can be realized during cast aluminum wheel manufacturing operations. Included is a conventional approach of conducting certain operations, including heating and transport, in a batch processing approach One might consider that this is an efficient approach in that multiple cast wheel blanks in close proximity to each other positively influence the temperature of each so as to maintain a desired temperature level. However, it has come to be appreciated in conjunction with the present invention that batch processing of this type can actually lead to inconsistencies in heat content and temperature gradients from wheel blank to wheel blank within a batch container such as a basket or tray.
In proceeding in accordance with the present invention, it has been determined that increased efficiencies in operation and energy conservation can be practiced during manufacturing of cast aluminum vehicle wheels while at the same time improving functional and strength characteristics of the resulting cast aluminum wheels. This facilitates achieving important design and strength objectives for cast aluminum vehicle wheels.